Methods and systems for calibrating a camera

ABSTRACT

A computer implemented method for calibrating a camera comprises the following steps carried out by computer hardware components: activating a subset of a plurality of light sources according to a plurality of activation schemes, wherein each activation scheme indicates which of the plurality of light sources to activate; capturing an image for each activation scheme using the camera; and calibrating the camera based on the captured images.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European Patent Application Number20151132.6, filed Jan. 10, 2020, the disclosure of which is herebyincorporated by reference in its entirety herein.

TECHNICAL FIELD

The present disclosure relates to methods and systems for calibrating acamera, and in particular to methods and systems for calibrating acamera provided in a vehicle.

BACKGROUND

Digital imaging devices, such as digital cameras, are used in variousautomotive applications. Calibration of the digital cameras may becumbersome.

For example, in current approaches, either multiple settings of thecamera versus a target or one image from a single setting of camera maybe used. In either of two methods, a high number of characteristic‘points’ may be required, for example in the form of circles or squaresin precisely known locations to compute a space relation of thoseobjects to the camera. This may put high requirements on the imagequality and on the precision of the setup. Current automotive cameras,may use imagers (for example cameras or image sensors) with 4 k orbetter resolution, a lens field-of-view may be from a few degrees tomore than 150 degrees with diaphragm aperture below f/2, and ahyperfocal distance may be in the range from 10 m to hundreds of meters.This may put high and practically unacceptable requirements on thecalibration equipment, both regarding to the required precision andspace and to the calibration time. Solutions including special immediateoptics or collimators increase price of the calibration setup and at thesame time reduce achievable precision.

Accordingly, there is a need to provide efficient methods and systemsfor calibrating a camera.

SUMMARY

The present disclosure provides a computer implemented method, acomputer system and a non-transitory computer readable medium accordingto the independent claims. Embodiments are given in the subclaims, thedescription and the drawings.

In one aspect, the present disclosure is directed at a computerimplemented method for calibrating a camera, the method comprising thefollowing steps performed (in other words: carried out) by computerhardware components: activating a subset of a plurality of light sourcesaccording to a plurality of activation schemes, wherein each activationscheme indicates which of the plurality of light sources to activate;capturing an image for each activation scheme using the camera; andcalibrating the camera based on the captured images.

In other words, a plurality of light sources is provided, and severalimages may be captured by the camera, wherein in each image one or moreof the light sources is activated and the other light sources are notactivated. In each image, the subset of light sources which is activatedmay be different. These images may then be used for calibration of thecamera.

For example, the method may be a method for calibration of a vehiclesensing camera.

The light sources may include lights, which may be lights of apre-determined wavelength range, or which may be light emitting diodesof a pre-determined wave length. All light sources may emit light of thesame wavelength or wavelength range, or the light sources may havedifferent wavelength ranges or wavelengths, so that the different lightsources may be distinguished by their color.

Various methods for calibrating may be used. Conventional methods whichusually are based on various images with different content may beapplied to the plurality of captured images showing different lightsources activated in each image. These images may be captured in anautomated manner by synchronizing the steps of activating the lightsources and capturing the image. Methods that could be used for thecalibration are for an example Zhan method or Tsai method or other usingmultiple points on the single image.

According to another aspect, at least one activation scheme comprises anindication of one light source of the plurality of light sources at atime. By activating only one light source at a time, there may be nointerference between the light sources, i.e. the light captured by thecamera may unambiguously be assigned to the light source.

According to another aspect, at least one activation scheme comprises anindication of a plurality of light source at a time. By activating morethan one light source at a time, more information may be acquired byeach captured image, which may reduce the overall calibration time.

According to another aspect, the plurality of light sources at a timeare at least a pre-determined distance apart when seen from the angle ofthe camera. This may avoid interference of the light sources, so thatthe light captured by the camera may unambiguously be assigned to therespective light source, even when more than one light source isactivated at a time.

According to another aspect, capturing the image for each activationscheme comprises capturing an image of the plurality of light sources.

According to another aspect, the plurality of light sources are providedin a three-dimensional space according to a pre-determined (i.e. known)spatial relationship amongst each other, and in a pre-determined (i.e.known) spatial relationship to the camera. The light sources may beprovided in locations which are not on a single line or not on a singletwo-dimensional plane, so that the full variety of the three-dimensionalspace may be used.

According to another aspect, the computer implemented method furthercomprises the following steps carried out by the computer hardwarecomponents: determining positions of the activated light sources in thecaptured images. For example, the images may be captured with the lightsources out of focus, which may reduce the required distance between thecamera and the light sources, and the respective positions may then bedetermined based on a center of the blurry (due to defocused capturing)light spots in the captured images.

According to another aspect, the positions in the captured images aredetermined based on a method for identification of candidate points aspossible characteristic points of a calibration pattern within an imageof the calibration pattern, the method for identification of candidatepoints comprising the steps of: determining spots within a filteredimage derived from the image of the calibration pattern, with a spotbeing defined as a coherent set of pixels of the filtered image havingpixel values exceeding a threshold, for each determined spot calculatinga central point of the determined spot, and identifying as candidatepoints all calculated central points, wherein the step of determiningthe spots comprises scanning the filtered image one pixel of thefiltered image after another. According to a further aspect, if ascanned pixel has a pixel value exceeding the threshold, the scanning ispaused and a spot contour tracing is executed starting with the lastscanned pixel as current pixel and the second last pixel as previouspixel, the spot contour tracing comprising as a tracing step the stepsof logging the current pixel as a contour pixel, and the method foridentification of candidate points further comprises the steps of: forneighboring pixels adjacent to the current pixel, evaluating thecondition, whether both the neighboring pixel has a pixel valueexceeding the threshold and another neighboring pixel, which immediatelyprecedes this neighboring pixel with respect to a sense of rotationaround the current pixel, has a pixel value not exceeding the threshold,selecting from all neighboring pixels, for which the condition isfulfilled, the neighboring pixel farthest from the previous pixel withrespect to said sense of rotation, and defining the current pixel asprevious pixel and defining the selected neighboring pixel as currentpixel; the spot contour tracing further comprising the steps ofrepeating the tracing step until the current pixel is again equal to thelast scanned pixel, determining the spot as the set of pixels comprisingthe logged contour pixels and the pixels surrounded by the loggedcontour pixels.

A gravity point of the blurred light point may then be determined as thecenter of gravity of the pixels surrounded by the contour pixels.

According to another aspect, calibrating the camera comprisesdetermining at least one intrinsic camera parameter or at least oneextrinsic camera parameter or at least one distortion parameter.

For example, the at least one intrinsic parameter comprises at least oneof a focal length of the camera, a sensitivity of the camera, or anaperture of the camera. For example, the at least one extrinsicparameter comprises at least one of a position of the camera in space oran orientation of the camera in space. For example, the at least onedistortion parameter comprises at least one of a defocus parameter ofthe camera, a spherical aberration parameter of the camera, a comaparameter of the camera, an astigmatism parameter of the camera, a fieldcurvature parameter of the camera, or an image distortion parameter ofthe camera.

In another aspect, the present disclosure is directed at a computersystem, said computer system comprising a plurality of computer hardwarecomponents configured to carry out several or all steps of the computerimplemented method described herein.

The computer system may comprise a plurality of computer hardwarecomponents (for example a processing unit, at least one memory unit andat least one non-transitory data storage). It will be understood thatfurther computer hardware components may be provided and used forcarrying out steps of the computer implemented method in the computersystem. The non-transitory data storage and/or the memory unit maycomprise a computer program for instructing the computer to performseveral or all steps or aspects of the computer implemented methoddescribed herein, for example using the processing unit and the at leastone memory unit.

According to another aspect, the computer system further comprises theplurality of light sources. For example, the plurality of light sourcesare provided in a three-dimensional space according to a pre-determinedspatial relationship amongst each other, and in a pre-determined spatialrelationship to the camera.

According to another aspect, the computer system further comprises astorage medium configured to store the captured images.

In another aspect, the present disclosure is directed at anon-transitory computer readable medium comprising instructions forcarrying out several or all steps or aspects of the computer implementedmethod described herein. The computer readable medium may be configuredas: an optical medium, such as a compact disc (CD) or a digitalversatile disk (DVD); a magnetic medium, such as a hard disk drive(HDD); a solid state drive (SSD); a read only memory (ROM), such as aflash memory; or the like. Furthermore, the computer readable medium maybe configured as a data storage that is accessible via a dataconnection, such as an internet connection. The computer readable mediummay, for example, be an online data repository or a cloud storage.

The present disclosure is also directed at a computer program forinstructing a computer to perform several or all steps or aspects of thecomputer implemented method described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments and functions of the present disclosure aredescribed herein in conjunction with the following drawings, showingschematically:

FIG. 1 a calibration system according to various embodiments;

FIG. 2A an illustration of a captured image showing multiplenon-interfering blurred light points;

FIG. 2B an illustration of an enlarged portion of a captured image witha single blurred light point with a computed gravity point according tovarious embodiments; and

FIG. 3 a flow diagram illustrating a method for calibrating a cameraaccording to various embodiments.

DETAILED DESCRIPTION

FIG. 1 shows a calibration system 100 according to various embodiments.A plurality of light points 104 may be provided in a 3D space 102. Forexample, the light points 104 may be small circular light points 104,and there may be provided between ten and several thousand light points104. Each of the light points 104 may be individually controlled by acontroller 108 (for example a computer). The location of the points 104may be known relative to each other and relative to the estimatedposition of a camera 106. The camera 106 may be looking at the 3D space102 the light points 104, and may be capturing a series of images (forexample a movie) while the controller 108 switches on and off one ormore of the light points 104 at the same time. The images captured bythe camera 106 may be analyzed to produce intrinsic or extrinsiccalibration data. The images captured by the camera 106 may be analyzedonline (i.e. during the operation of the lights) or may be recorded (forexample in a storage provided in the controller 108 or attached to thecontroller 108, or an external media) for analysis on the same ordifferent equipment (i.e. for later analysis using the controller 108,or for analysis using a device different from the controller 108).

With the system as illustrated in FIG. 1 , a single pose multi imagecalibration may be provided. For example, the calibrated camera may be asafety and road assistance camera.

According to various embodiments, the plurality of light sources may beprovided in a fixed arrangement, so that the respective relativepositions of the plurality of light sources may be fixed and known. Thearrangement may then be provided at a single position (with a relativeposition in 2D or 3D) relative to the camera, so that the plurality ofimages may be captured without moving the arrangement. The distance fromthe camera to the arrangement (which may also be referred to as acalibration field) may be well below the hyperfocal distance of thecamera.

The captured images may be provided as a sequence of 2D or 3D images(showing (blurred) light points of the light sources) presented to thecamera with light points using wide spectra (‘white’), single color ormulti color points.

According to various embodiments, the calibration system and calibrationmethod may allow calibration of very wide (for example 100 degree orwider) automotive cameras or very narrow (for example 30 degree ornarrower) cameras in the limited space on the production line, where itmay be easier to get a space below 1.8 m/1.8 m/3 m than getting 10 m/10m/10 m or more. For narrow cameras (like for 28 degree where hyperfocaldistance is >50 m) this may be a matter of making precision calibrationpractically ‘doable’ or ‘impractical’.

According to various embodiments, the calibration system and method maybe applied at limited spaces, even for large image field where usuallylarge distances from the camera are required. According to variousembodiments, not sharp images may be used with the assumption thatcircular light points are seen by the camera in this case as distortedcircles. Since not all the points are activated (in other words:switched on) at the same time, distribution of the light from a singlepoint to the pixels on the captured image may be measured and it may becomputed where the light was originally located in the projection (andhence in the 3D space relative to the camera). This may be done for eachand every light point separately or in groups of light points if thosedo not interfere with each other (for example, if these light points aresufficiently spaced apart, as illustrated in FIG. 2A below, or if theselight points have different colors, i.e. when the respective lightsources emit light of different wavelengths or different wavelengthranges).

FIG. 2A shows an illustration 200 of a captured image showing multiplenon-interfering blurred light points 202, 204, 206, 208 according tovarious embodiments.

FIG. 2B shows an illustration 250 of an enlarged portion of a capturedimage with a single blurred light point 252 with a computed gravitypoint 254 according to various embodiments.

Each of light points in a captured image (for example in an imager ofthe camera) may allow computing the central point (in other words: thecenter of gravity) of the light point so that the same type of theinformation may be obtained as if a sharp image (i.e. an image in focus)would be captured, even if the light sources are out of focus. Themethod to find those points may be identical or similar to the methodprovided in WO/2017/093037, for example with the change for thecorrelation image to a circle or as a ‘gravity point’ approachsurrounded by the ‘equipotential plate’. As the result of this process,the location of the complete set of points may be obtained from multipleexposures but at one position. Those locations may be then used in theusual way in the calibration. As the end result, calibration values (forexample both intrinsic and extrinsic) may be obtained after analysis ofthe series of the imaged (or pictures) taken (or acquired) from onesingle location of the camera while the size of the field (i.e. the 3Dspace where the light sources are required) may be small, for examplearound 1.5 m/1.5 m/1.5 m and the distance to the camera may be dependenton the focal length but well below required in currently existingcalibration methods.

According to various embodiments, light switching (i.e. selectiveactivation of one or more light sources) may be synchronized with thecamera operation, for example by close loop operation (where lightsources are activated and then the image is captured, and then it may beproceeded to the next combination (or activation scheme) of active lightsources) or by an open loop method (where only the approximate framefrequency may need to be known to synchronize the activation of thelight sources and the capturing of the images, and where it may bestarted with the light sources switched off, and then for each step, thecombination of light sources may be set, then it may be waited for apre-determined frame period (for example for 3 frame periods), and itmay then be proceeded to the next step (with the next activationscheme), wherein the last step may be to switch off all the lightsources).

The sequence of activation of the light sources (in other words: theactivation schemes) may be changed, but may be longer when there aresingle wavelength light sources only. In the analysis of captured images(which may be in the data format of video frames), it may be looked forthe central frame between the change of the visible combination of lightsources. In an example with 30 frames per second and 5 light sourcesbeing visible at the same time, and the field having 500 points (inother words: 500 light sources), the measurements (in other words: thecapturing of the images) may be done in 10 seconds. This may be speededup using multiple colors of the light sources for a color camera, sothat even partially interfering points may be discriminable by theircolors. With the previous conditions and three basic colors in theimager matrix (of the camera), the measurement may for example be donewith in about 3.3 seconds for a simple scheme, and with a more complexscheme (three colors in shifted phases) the time may go down to about 3seconds or lower. The difference between the simpler scheme (in otherwords: the ‘longer’ or slower method) and the more complex scheme (inother words: the ‘shorter’ or faster method) depends on the camera beingcapable to distinguish colors. In such case there may be two partiallyoverlapping points with distinct primary colors which may be properlydetectable, and the impact from each color may be properly deducted.

At the same time, issues with elimination of the color mosaic from thepictures may be reduced or avoided. The color mosaic in the imager isusually eliminated in the process of the point detection process. Whenmultiple colors in the light sources are used, elimination of the mosaicmay be easier, since light source correlate with colors on the imagercolor mask, even if different sets of colors are used.

FIG. 3 shows a flow diagram 300 illustrating a method for calibrating acamera according to various embodiments. At 302, a subset of a pluralityof light sources may be activated according to a plurality of activationschemes, wherein each activation scheme indicates which of the pluralityof light sources to activate. At 304, an image may be captured for eachactivation scheme using the camera. At 306, the camera may be calibratedbased on the captured images.

According to various embodiments, at least one activation schemecomprises an indication of one light source of the plurality of lightsources at a time. According to various embodiments, at least oneactivation scheme comprises an indication of a plurality of light sourceat a time.

According to various embodiments, the plurality of light sources at atime are at least a pre-determined distance apart when seen from theangle of the camera.

According to various embodiments, capturing the image for eachactivation scheme comprises capturing an image of the plurality of lightsources.

According to various embodiments, the plurality of light sources areprovided in a three-dimensional space according to a pre-determinedspatial relationship amongst each other, and in a pre-determined spatialrelationship to the camera.

According to various embodiments, the method may further comprisedetermining positions of the activated light sources in the capturedimages.

According to various embodiments, the positions in the captured imagesare determined based on a method for identification of candidate pointsas possible characteristic points of a calibration pattern within animage of the calibration pattern, the method for identification ofcandidate points comprising the steps of: determining spots within afiltered image derived from the image of the calibration pattern, with aspot being defined as a coherent set of pixels of the filtered imagehaving pixel values exceeding a threshold, for each determined spotcalculating a central point of the determined spot, and identifying ascandidate points all calculated central points, wherein the step ofdetermining the spots comprises scanning the filtered image one pixel ofthe filtered image after another, wherein, if a scanned pixel has apixel value exceeding the threshold, the scanning is paused and a spotcontour tracing is executed starting with the last scanned pixel ascurrent pixel and the second last pixel as previous pixel, the spotcontour tracing comprising as a tracing step the steps of logging thecurrent pixel as a contour pixel, for neighboring pixels adjacent to thecurrent pixel, evaluating the condition, whether both the neighboringpixel has a pixel value exceeding the threshold and another neighboringpixel, which immediately precedes this neighboring pixel with respect toa sense of rotation around the current pixel, has a pixel value notexceeding the threshold, selecting from all neighboring pixels, forwhich the condition is fulfilled, the neighboring pixel farthest fromthe previous pixel with respect to said sense of rotation, and definingthe current pixel as previous pixel and defining the selectedneighboring pixel as current pixel; the spot contour tracing furthercomprising the steps of repeating the tracing step until the currentpixel is again equal to the last scanned pixel, determining the spot asthe set of pixels comprising the logged contour pixels and the pixelssurrounded by the logged contour pixels.

According to various embodiments, calibrating the camera comprisesdetermining at least one intrinsic camera parameter or at least oneextrinsic camera parameter or at least one distortion parameter.

According to various embodiments, the at least one intrinsic parametercomprises at least one of a focal length of the camera, a sensitivity ofthe camera, or an aperture of the camera; wherein the at least oneextrinsic parameter comprises at least one of a position of the camerain space or an orientation of the camera in space; and wherein the atleast one distortion parameter comprises at least one of a defocusparameter of the camera, a spherical aberration parameter of the camera,a coma parameter of the camera, an astigmatism parameter of the camera,a field curvature parameter of the camera, or an image distortionparameter of the camera.

Each of the steps 302, 304, 306 and the further steps described abovemay be performed by computer hardware components.

What is claimed is:
 1. A method comprising: activating, by computerhardware components, a subset of light sources from a plurality of lightsources according to a plurality of activation schemes, wherein eachactivation scheme of the plurality of activation schemes indicates whichlight sources from the plurality of light sources to include in therespective subset of light sources; capturing, by a camera, an image ofeach subset of light sources for each activation scheme, a distancebetween the camera and the plurality of light sources being less than ahyperfocal distance of the camera, the light sources in each capturedimage being out-of-focus light sources; determining, based on respectivecenters of the out-of-focus light sources in each captured image,respective positions of the light sources relative to the camera in eachcaptured image; and calibrating the camera based on the positions of thelight sources in each captured image.
 2. The method of claim 1, whereinthe subset of light sources comprises: a single light source from theplurality of light sources; or multiple light sources from the pluralityof light sources.
 3. The method of claim 2, wherein the multiple lightsources at a time are at least a pre-determined distance apart when seenfrom an angle of the camera.
 4. The method of claim 1, wherein theplurality of light sources is provided in a three-dimensional spaceaccording to a pre-determined spatial relationship amongst each other,and in a pre-determined spatial relationship to the camera.
 5. Themethod of claim 1, wherein the positions of the light sources in thecaptured images are determined based on identification of candidatepoints as possible characteristic points of a calibration pattern withinan image of the calibration pattern by at least: determining spotswithin a filtered image derived from the image of the calibrationpattern, with a spot being defined as a coherent set of pixels of thefiltered image having pixel values exceeding a threshold, for eachdetermined spot calculating a central point of the determined spot, andidentifying as the candidate points all the calculated central points,wherein determining the spots comprises scanning the filtered imagederived from the image of the calibration pattern by scanning one pixelafter another.
 6. The method of claim 5, further comprising: responsiveto a scanned pixel having a pixel value exceeding the threshold, pausingthe scanning, and tracing a spot contour starting with the scanned pixelas a first current pixel, the tracing of the spot contour comprisinglogging the first current pixel as a contour pixel; evaluating acondition of neighboring pixels adjacent to the first current pixel, thecondition comprising whether the neighboring pixel has a pixel valueexceeding the threshold, and another neighboring pixel, whichimmediately precedes the neighboring pixel with respect to a sense ofclockwise or counterclockwise rotation around the first current pixel,has a pixel value not exceeding the threshold; selecting from allneighboring pixels, for which the condition is fulfilled, theneighboring pixel farthest from an immediate previously scanned pixel tothe first current pixel with respect to the sense of rotation; definingthe first current pixel as a previous pixel and defining the selectedneighboring pixel as a second current pixel; repeating the tracing ofthe spot contour until the first current pixel is again equal to thescanned pixel; and determining the spot of coherent pixels as a set ofpixels comprising the logged contour pixels and the pixels surrounded bythe logged contour pixels.
 7. The method of claim 1, wherein calibratingthe camera comprises determining at least one distortion parameter, theat least one distortion parameter comprises at least one of a defocusparameter of the camera, a spherical aberration parameter of the camera,a coma parameter of the camera, an astigmatism parameter of the camera,a field curvature parameter of the camera, or an image distortionparameter of the camera.
 8. The method of claim 1, wherein calibratingthe camera comprises: determining at least one intrinsic parameter,wherein the at least one intrinsic parameter comprises at least one of afocal length of the camera, a sensitivity of the camera, or an apertureof the camera; and determining at least one extrinsic parameter, whereinthe at least one extrinsic parameter comprises at least one of aposition of the camera in space or an orientation of the camera inspace.
 9. A computer system comprising computer hardware componentsconfigured to: activate a subset of light sources from a plurality oflight sources according to a plurality of activation schemes, whereineach activation scheme of the plurality of activation schemes indicateswhich light source of the plurality of light sources to include in therespective subset of light sources; capture, by a camera, an image ofeach subset of light sources for each activation scheme, a distancebetween the camera and the plurality of light sources being less than ahyperfocal distance of the camera, the light sources in each capturedimage being out-of-focus light sources; determine, based on respectivecenters of the out-of-focus light sources in each captured image,respective positions of the light sources relative to the camera in eachcaptured image; calibrate the camera based on the positions of the lightsources in each captured image at least one intrinsic parameter and theat least one extrinsic parameter.
 10. The computer system of claim 9,further comprising the plurality of light sources.
 11. The computersystem of claim 10, wherein the plurality of light sources is providedin a three-dimensional space according to a pre-determined spatialrelationship amongst each other, and in a pre-determined spatialrelationship to the camera.
 12. The computer system of claim 9, furthercomprising a storage medium configured to store the captured images. 13.The system of claim 9, wherein the computer hardware components areconfigured to determine the positions of each light source in thecaptured images based on identification of candidate points as possiblecharacteristic points of a calibration pattern within an image of thecalibration pattern by at least: determining spots within a filteredimage derived from the image of the calibration pattern, with a spotbeing defined as a coherent set of pixels of the filtered image havingpixel values exceeding a threshold, for each determined spot calculatinga central point of the determined spot, and identifying as the candidatepoints all the calculated central points, wherein determining the spotscomprises scanning the filtered image derived from the image of thecalibration pattern by scanning one pixel after another.
 14. The systemof claim 13, wherein the computer hardware components are furtherconfigured to: responsive to a scanned pixel having a pixel valueexceeding the threshold, pausing the scanning, and tracing a spotcontour starting with the scanned pixel as a first current pixel, thetracing of the spot contour comprising logging the first current pixelas a contour pixel; evaluating a condition of neighboring pixelsadjacent to the first current pixel, the condition comprising whetherthe neighboring pixel has a pixel value exceeding the threshold, andanother neighboring pixel, which immediately precedes the neighboringpixel with respect to a sense of clockwise or counterclockwise rotationaround the first current pixel, has a pixel value not exceeding thethreshold; selecting from all neighboring pixels, for which thecondition is fulfilled, the neighboring pixel farthest from an immediatepreviously scanned pixel to the first current pixel with respect to thesense of rotation; defining the first current pixel as a previous pixeland defining the selected neighboring pixel as a second current pixel;repeating the tracing of the spot contour until the first current pixelis again equal to the scanned pixel; and determining the spot ofcoherent pixels as a set of pixels comprising the logged contour pixelsand the pixels surrounded by the logged contour pixels.
 15. Anon-transitory computer readable medium comprising instructions thatwhen executed, configure computer hardware components to: activate asubset of light sources from a plurality of light sources according to aplurality of activation schemes, wherein each activation scheme of theplurality of activation schemes indicates which light source of theplurality of light sources to include in the respective subset of lightsources; capture, by a camera, an image of each subset of light sourcesfor each activation scheme, a distance between the camera and theplurality of light sources being less than a hyperfocal distance of thecamera, the light sources in each captured image being out-of-focuslight sources; determine, based on respective centers of theout-of-focus light sources in each captured image, respective positionsof the light sources relative to the camera in each captured image; andcalibrate the camera based on the positions of the light sources in eachcaptured image at least one intrinsic parameter and the at least oneextrinsic parameter.
 16. The non-transitory computer readable medium ofclaim 15, wherein the subset of light sources comprises: a single lightsource from the plurality of light sources; or multiple light sourcesfrom plurality of light sources.
 17. The non-transitory computerreadable medium of claim 16, wherein the multiple of light sources at atime are at least a pre-determined distance apart when seen from anangle of the camera.
 18. The non-transitory computer readable medium ofclaim 15, wherein the instructions, when executed, configured thecomputer hardware components to capture the image for each activationscheme by capturing an image of the plurality of light sources.
 19. Thenon-transitory computer readable medium of claim 15, wherein theplurality of light sources is provided in a three-dimensional spaceaccording to a pre-determined spatial relationship amongst each other,and in a pre-determined spatial relationship to the camera.
 20. Thenon-transitory computer readable medium of claim 15, wherein theinstructions, when executed, configure the computer hardware componentsto determine the positions of each light source in the captured imagesbased on identification of candidate points as possible characteristicpoints of a calibration pattern within an image of the calibrationpattern by at least: determining spots within a filtered image derivedfrom the image of the calibration pattern, with a spot being defined asa coherent set of pixels of the filtered image having pixel valuesexceeding a threshold, for each determined spot calculating a centralpoint of the determined spot, and identifying as the candidate pointsall the calculated central points, wherein determining the spotscomprises scanning the filtered image derived from the image of thecalibration pattern by scanning one pixel after another.